The present invention relates to a substrate sheet formed with external electrodes, wiring, and probing electrodes on one surface, a manufacturing method of a circuit substrate using the substrate sheet and an ink jet head equipped with the circuit substrate.
The ink jet head records an image such as a character and pattern on a recording paper by ejecting an ink from its nozzle hole, while moving relatively to the recording paper. A plurality of lines of lined-up nozzle holes along a moving direction of the recording paper are arranged in parallel. The ink jet head comprises a cavity plate on which a channel is formed for feeding ink to each nozzle hole. In addition, the ink jet head is layered on the cavity plate, and comprises a plate-like actuator (such as a piezoelectric device) for ejecting ink from each nozzle hole, respectively. Further, the ink jet head comprises a circuit substrate layered on the actuator, for connecting the actuator and an IC chip that drives the actuator.
An individual electrode corresponding to each nozzle hole and an earth electrode for earthing are formed on one surface of the actuator. A drive signal for driving the actuator is given to the individual electrode, through an external electrode formed on the circuit substrate (see Japanese Patent Publication No. 3270197).
FIG. 1 is a plan view showing a construction of a conventional circuit substrate (Japanese Patent Application Laid-Open No. 2003-80683). The circuit substrate is formed by arranging an IC chip 80, a terminal part 81 and an electrode part 82 on an substantially rectangular flexible insulating film 8 made of polyimide. In the insulating film 8, the width of one end in a longitudinal direction of the insulating film 8 is larger than the width of the other end. The aforementioned one end is called a wide portion, and the other end is called a narrow portion, hereafter.
The IC chip 80 is mounted on a center of the wide portion, and the terminal part 81 is formed at a tip side in the length direction of the wide portion. The IC chip 80 outputs the drive signal to the actuator. In addition, an electric power and a signal for outputting the drive signal, or the like is supplied to the IC chip 80, through the terminal part 81.
Electrode parts 82 are formed in the narrow portion layered on one surface of the actuator. The electrode parts 82 are connected to the individual electrode and the earth electrode provided on one surface of the actuator. The electrode parts 82 are provided in parallel at both ends in a direction of the width of the narrow portion of the insulating film 8. External electrodes 24a, 24a, 14a, 14a, . . . 24a, 24a and external electrodes 24b, 24b, 14b, 14b, . . . , 24b, 24b are provided in this order, respectively as the electrode parts 82. Each external electrode 14a and 14b has an approximately square shape, and is connected to the individual electrode of the actuator. The external electrodes 14a, 14b are connected to the IC chip 80 through wirings 18a, 18b, respectively. The external electrodes 24a, 24b have an approximately square shape, and are connected to the earth electrode of the actuator. The external electrodes 24a, 24b are connected to the terminal part 81 through wirings 28a, 28b, respectively.
FIG. 2, FIG. 3 and FIG. 4 are explanatory views of the manufacturing method of the conventional circuit substrate.
On a belt-like substrate sheet 90, a plurality of substantially rectangular regions 900 corresponding to the insulating film 8 of the circuit substrate are arranged in parallel in a lengthwise direction of the substrate sheet 90, so that the lengthwise direction of each region 900 is coincided with a widthwise direction of the substrate sheet 90. As will be described later, the circuit substrate is formed by cutting the substrate sheet 90 along outlines of the regions 900. Hereafter, one region 900 will be explained.
Belt-like extending conductors 16a, 26a and extending conductors 16b, 26b are provided in a state of extending to outside the regions 900 in widthwise directions of the regions 900 from the external electrodes 14a, 24a and the external electrodes 14b, 24b, respectively. An extending direction of each extending conductor 16a, 26a from each external electrode 14a, 24a, and an extending direction of each extending conductor 16b, 26b from each external electrode 14b, 24b are opposite to each other.
The width (width in a direction orthogonal to the extending direction) of each extending conductor 16a, 16b, 26a, 26b is approximately equal to the width of each external electrode 14a, 14b, 24a, 24b, and set at about 0.12 mm.
Substantially rectangular probing electrodes 15a, 15b, 25a, 25b connected to each external electrode 14a, 14b, 24a, 24b through each extending conductor 16a, 16b, 26a, 26b are formed outside the regions 900. The width of each probing electrode 15a, 15b, 25a, 25b is set larger than the width of each extending conductor 16a, 16b, 26a, 26b, and set at about 0.2 mm.
Each probing electrode 15a, 15b, 25a, 25b is used in a conduction test of each external electrode 14a, 14b, 24a, 24b, the IC chip 80, and the terminal part 81.
On the substrate sheet, solder H, which is a conductive brazing material for connecting each external electrode 14a, 14b, 24a, 24b and the actuator, is adhered to the surface of each external electrode 14a, 14b, 24a, 24b, before the circuit substrate is formed. In addition, the solder H for connecting the terminal part 81 and an external connector is adhered to the terminal part 81.
Therefore, the substrate sheet moves in the lengthwise direction (in a direction shown by hollow arrow in the figure) of the substrate sheet, with a surface (referred to as an electrode forming face hereafter) on which each external electrode 14a, 14b, 24a, 24b and the terminal part 81 are formed, faced downside, and passes over solder tanks M3, M3 for blowing up solder previously heated and fused, for each external electrode 14a, 14b, 24a, 24b and the terminal part 81. However, a part, on which the IC chip 80 is mounted, does not pass over the solder tank M3.
The solder is hardly adhered to the insulating film 8, and meanwhile, the solder is adhered to the surface of each external electrode 14a, 14b, 24a, 24b, each probing electrode 15a, 15b, 25a, 25b, and each extending conductor 16a, 16b, 26a, 26b, and the terminal part 81. The solder H thus adhered thereto is cured once. Then, the solder H thus adhered is heated and fused again, at the time point of connecting the individual electrode, the earth electrode, and each external electrode 14a, 14b, 24a, 24b, and at the time point of connecting the connector and the terminal part 81.
The conduction test is performed before or after adhesion of solder H. After completing the conduction test, the substrate sheet is cut along the outline of the region 900, before being connected to the actuator. Thus, the circuit substrate including each external electrode 14a, 14b, 24a, 24b, and not including each probing electrode 15a, 15b, 25a, 25b and each extending conductor 16a, 16b, 26a, 26b is formed. The substrate sheet is cut at a connection part (shown by two dot chain line in FIG. 3) of each external electrode 14a, 14b, 24a, 24b, and each extending conductor 16a, 16b, 26a, 26b, for example.